Calcium phosphate materials including hydroxyapatite and tricalcium phosphate are widely used as living hard tissue replacements such as artificial bones and dental roots because their sintered bodies are non-toxic and likely to bond with the bone in a living system. Sintered calcium phosphate, however, is not necessarily satisfactory in practice because it is neither mechanically strong nor tough. Sintered calcium phosphate tends to break or chip away when it is shaped to a configuration conforming to a deficient site in a living system, implanted and embedded in the site.
Japanese Patent Application Kokai No. 57971/1984 discloses fibrous or acicular apatite which is reinforced with mineral fibers. This composition, however, is impractical in that manufacture of apatite in fiber or needle form is very difficult and mineral fibers having affinity thereto must be separately prepared. It is a cumbersome operation to sinter apatite in close contact with mineral fibers under pressure at a relatively low temperature of lower than 800.degree. C. under conditions to prevent substantial escape of moisture. In addition, such low temperature sintering results in a low relative density. Many problems must be overcome before this composition can be used in practice.
Japanese Patent Application Kokai No. 162676/1987 discloses a composite apatite material of whisker reinforcement type in which mullite whiskers are simultaneously grown during sintering of apatite. Simple precipitation of mullite whiskers, however, will result in a sintered body which is not strong or tough enough to prevent chipping and cracking upon implantation, that is, application to a deficient site in a living system.
Also, whisker-reinforced sintered bodies are known from Japanese Patent Application Kokai No. 151652/1988 disclosing a sintered body which is reinforced with SiC whiskers using a hot isostatic press (HIP) technique and Japanese Patent Application Kokai No. 27308/1988 disclosing the use of various mineral whiskers. In the former, sintering is carried out in the presence of sintering aids, but to an unsatisfactory degree of reinforcement because no measure is taken such that the sintering aids may control the interface between the whiskers and the matrix. In the latter, the mixture must be sintered at relatively low temperatures so that the whiskers and the matrix may not react with each other because it is difficult to properly control the interface between the whiskers and the matrix. Then no satisfactory reinforcement can be achieved.
It is thus desired to eliminate the drawbacks of prior art whisker-reinforced calcium phosphate sintered bodies.